Experimental studies will be undertaken to explore aspects of the pathophysiology of five clinical conditions common to infants and children: respiratory distress syndrome, lead intoxication, interstitial nephritis, ureteral obstruction, and renal transplantation. 1. Metabolic acidosis is an important disturbance in infants with respiratory distress syndrome. The role of the kidney in ameliorating or contributing to the acidosis is unclear. Studies will be performed in neonatal puppies to study the renal effects of hypoxia, hypercapnia, and positive pressure respiration on renal hemodynamics, conservation of sodium and water, and capacity to reabsorb bicarbonate and excrete net acid. 2. We hypothesize that tubular lesions induced by exposure to lead in early life lead to hypertension and chronic renal disease in adulthood. Fractional reabsorption in the proximal tubule, and the intrinsic reabsorptive capacity for Na will be measured by micropuncture techniques in lead intoxicated rats. Correlates will be sought between sodium reabsorption, water balance, plasma renin activity, and blood pressure. The effect of chelation therapy on these variables and on GFR will be tested. 3. The mechanism causing a decrease in GFR in patients with interstitial nephritis is unknown. We will explore this problem in an immunological model of tubulointerstitial disease secondary to antitubular basement membrane antibody in guinea pigs. Variables to be measured will be whole kidney GFR, superficial cortical single nephron GFR, renal blood flow, filtration fraction, and fractional reabsorption of water and sodium. 4. A guinea pig model of hereditary congenital ureteral obstruction will be utilized to determine functional changes in the obstructed kidney and reversibility with relief of obstruction at different times post-natally. In other studies, ureters will be obstructed post-natally to determine effects on ureteral morphology and function and reversibility of these lesions. 5. Renal transplantation utilizing infant rats as donors and adult rats as recipients, will be done, as a model of the clinical situation in which children serve as donors for adult patients. The ability of these kidneys to grow and adapt functionally will be studied.